1. Field of the Invention
The present invention pertains to the field of expansible chamber motors or devices having a bellows and having a shaft axis parallel to the axis of the working member.
2. Description of the Related Art
Rotary actuators in which an output member is driven to rotate through a portion of a circle by fluid pressure to actuate a valve or the like are well-known. Some prior art devices of this kind use a linearly moving piston with a crank, gears, or a swashplate to convert the piston motion into the desired rotary motion and are relatively bulky, heavy, and expensive because of the motion converting elements and the necessary machine work and dynamic fluid seals. Other prior art devices of this kind use pivoting vanes and are simpler and more compact, but still require machine work and fluid seals. These disadvantages are particularly serious where only one-shot operation is required. It is, therefore, highly desirable to provide an actuator that directly converts fluid pressure into rotary motion and that does not require machining or fluid seals.
Some of the disadvantages of weight, bulk, and expense of fluid pressure driven actuators are avoided, particularly for one-shot operation, in bellows devices pressurized by pyrotechnically generated gas which may be provided by a charge and igniter integrally constructed with the bellows. However, such bellows devices heretofore have only provided linear motion.
A bellows device for direct conversion of fluid pressure to rotary motion is shown in U.S. Pat. No. 4,108,050 to Paynter. This rotary operator device uses a thin shell of elastomeric material with inextensible strands bonded to the shell and, together with the shell, fixed to coupling members at the shell ends. The shell and strands are twisted into a helically fluted configuration so that, when the shell is pressurized, the shell bows outward and the strands urge the coupling members to rotate relatively to each other. The rotary operator includes an external frame or an internal axle, apparently to keep the flexible shell and strands from buckling. In relation to the linear motion bellows devices mentioned above, the construction of this rotary operator is more complex and it is bulkier and heavier. Also, the shell of elastomeric material is stated to be for operation to 220.degree. F. (104.degree. C.) and is thus not well-suited to the temperatures of pyrotechnically generated gas.
For pressure measurement, it is well-known to use a straight, metallic Bourdon tube twisted about its axis, the tube tending to untwist when subjected to an internal pressure to be measured. Such a tube may be a twisted, flattened tube or may have helical flutes. The construction of such tubes is optimized for pressure measurement and the elastic limit of the tube cannot be exceeded in normal operation. As a result, such tubes typically have motion limited to a small angle, only provide a minuscule torque, and are axially bulky since their axial length is relatively great in relation to their diameter.